<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <link rel="stylesheet" href="./reset.css">
  <style>
    
    body{
      border: 1px solid red;
      height: 500px;
    }
    .box{
      background: red;
      margin: 100px;
     width: 300px;
     height: 300px;
      /* width: 20%;
      min-width: 100px;
      height: 100px;
      float: left; */
      /* margin-left:100px;
      display: inline; */
      /* margin: 200px;
      overflow:hidden; */

      
      /* -moz-border-radius:50%;
      -webkit-border-radius:50%;
      -o-border-radius:50%;
      -ms-border-radius:50%;
      border-radius: 50%; */

    }

    /* 根据屏幕的宽度，让不同的样式生效 */
    @media screen and (min-width:700px) and (max-width: 1000px) {
    body {
        background-color:lightblue;
    } 
    .box{
        width: 200px;
        height: 200px;
    }
}

@media screen and (min-width: 400px) and (max-width: 700px) {
    body {
        background-color:gold;
    } 
    .box{
        width: 100px;
        height: 100px;
    }
}

@media screen and (max-width: 400px) {
    body {
        background-color:blueviolet;
    } 
    .box{
        width: 50px;
        height: 50px;
    }
}


a:hover {color:blue}
a:active {color:pink}
a:visited {color:green}
a:link {color: red;}

  </style>
</head>
<body>
  
  <div class="box"></div>

  <a href="https://www.baidu.com">百度</a>
</body>
</html>